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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 6 | Copyright

Special issue: Flow in complex terrain: the Perdigão campaigns (WES/ACP/AMT...

Atmos. Meas. Tech., 11, 3801-3814, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 28 Jun 2018

Research article | 28 Jun 2018

Wind turbine wake measurements with automatically adjusting scanning trajectories in a multi-Doppler lidar setup

Norman Wildmann1, Nikola Vasiljevic2, and Thomas Gerz1 Norman Wildmann et al.
  • 1Deutsches Zentrum für Luft- und Raumfahrt e.V., Münchner Str. 20, Oberpfaffenhofen, Germany
  • 2DTU Wind Energy, Technical University of Denmark, Frederiksborgvej 399, Building 118-VEA, 4000 Roskilde, Denmark

Abstract. In the context of the Perdigão 2017 experiment, the German Aerospace Center (DLR) deployed three long-range scanning Doppler lidars with the dedicated purpose of investigating the wake of a single wind turbine at the experimental site. A novel method was tested for the first time to investigate wake properties with ground-based lidars over a wide range of wind directions. For this method, the three lidars, which were space- and time-synchronized using the WindScanner software, were programmed to measure with crossing beams at individual points up to 10 rotor diameters downstream of the wind turbine. Every half hour, the measurement points were adapted to the current wind direction to obtain a high availability of wake measurements in changing wind conditions. The linearly independent radial velocities where the lidar beams intersect allow the calculation of the wind vector at those points. Two approaches to estimating the prevailing wind direction were tested throughout the campaign. In the first approach, velocity azimuth display (VAD) scans of one of the lidars were used to calculate a 5min average of wind speed and wind direction every half hour, whereas later in the experiment 5min averages of sonic anemometer measurements of a meteorological mast close to the wind turbine became available in real time and were used for the scanning adjustment. Results of wind speed deficit measurements are presented for two measurement days with varying northwesterly winds, and it is evaluated how well the lidar beam intersection points match the actual wake location. The new method allowed wake measurements to be obtained over the whole measurement period, whereas a static scanning setup would only have captured short periods of wake occurrences.

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Short summary
Wind turbines extract energy from the flow which manifests in a region of lower wind speeds and increased turbulence downstream of the rotor, the so-called wake. Understanding the characteristics of the wake is a key challenge for wind-energy research. A new strategy for measuring the wind in the wake with three synchronized lidar instruments is presented. The measurement points are automatically adapted to the prevailing wind direction to achieve continuous monitoring of wake properties.
Wind turbines extract energy from the flow which manifests in a region of lower wind speeds and...